The Lions found scoring difficult at Kingsway on Saturday, lasting 74.2 overs but making just 173.
The Roos would have been confident in eclipsing the total but lost Aaron Brunner and Mitch McGee in the final 17 overs of the day to leave the hosts shaky on 2-40.
Wanneroo bowler Mathew Dzodzos dominated to take 5-37, while the visitors’ Aaron Lilly top scored with 54.
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READ NOWLions bowler James Sansalone took out both of the Roos’ openers to earn himself an impressive 2-9.
Play resumes with Christian Smith and Rob Richards at the crease this weekend.